Canadian Patent 1,000,000 issued Nov. 16, 1976 to James Guillet and Harvey Troth, corresponding to U.S. Pat. No. 3,860,538, discloses photodegradable polymers of vinyl aromatic monomers. Generally, the polymers are photodegradable polymers of styrene. The polymers are prepared by first preparing a copolymer of a vinyl aromatic monomer and a vinyl ketone. The copolymer is then blended, or let down with styrene polymer. The resulting polymer blend is photodegradable.
There is a growing concern over the degradability of plastics. While the polymers of the above noted patents do provide photodegradable plastics they do not provide a foamable bead which is suitable for the manufacture of closed-cell foamed products. In particular there is concern with disposable containers such as hot drink (coffee) cups and other containers for fast foods. Indeed, there is such concern that some jurisdictions, such as Florida, are contemplating bans on nondegradable plastic articles.
Generally, there are two method for making foamed polymers of vinyl aromatic monomers. Open celled foams may be prepared by an extrusion process. That is the polymer resin and a blowing agent are extruded and the blowing agent decomposes to yield a foamed polymer melt. Closed cell foamed articles are made by soaking small polymeric beads having a suitable particle size distribution in a suitable blowing agent such as pentane or hexane or halogenated hydrocarbons. The beads may be expanded together with a more environmentally friendly blowing agent such as nitrogen or carbon dioxide. Typically the polymer is made by a suspension process to provide the high surface ratio required to effectively permit the blowing agent to be taken up by the polymer. The impregnated beads are then partially expanded at low temperatures such as in steam. The partially expanded beads are then placed in a mold and further heated, again at relatively low temperatures to expand the beads and fuse the beads together to give a closed cell product. For containers closed cell construction is required as in open celled foams the contents leak through the foam. Unfortunately, the Guillet polymers are produced using conventional bulk polymerization technology which results in resin pellets which are of an inappropriate size for impregnation with blowing agent. Furthermore the technique of master batching Guillet polymers does not provide as homogenous a particle containing photodegradable polymer as those of the present invention.
While the Guillet patents have been available for some 20 years, there has, to the best of applicant's knowledge, been no attempt to manufacture suspension beads suitable for foaming using any of the Guillet technology. The present invention produces polymer particles having an appropriate particle size distribution in a high yield.
The present invention seeks to provide a foamable suspension polymer bead which is photodegradable. The present invention seek to provide a process for the manufacture of such beads and the present invention seeks to provide foamed containers made from such beads.